This invention relates generally to an anti-chatter circuit used to clean up the input produced by a mechanical contact closing switch and more particularly, to an anti-chatter circuit which discriminates between true switch inputs and inputs of electrical noise. Many circuits have been devised to provide clear square wave pulse inputs to a circuit upon the making of a connection between electrical contacts. The irregular waveform actually produced when the mechanical contacts come together is "smoothed over" in the anti-chatter circuit and a uniform output pulse is produced every time the contacts are brought together for an electrical connection. However, there is a possibility of erroneous circuit operation when electrical noises other than the switch input are introduced at the input terminal of the circuit. In a small sized portable apparatus such as an electronic watch, there has not been a problem because the conventional electronic watch includes no internal source of electrical noises. Further, the metal case of the watch shields the circuit input from the intrusion of externally generated electrical noises. However, electronic watches are becoming more and more versatile and complex and include such objects as loudspeakers and other electromechanical converters. Thus, there is a source for generating electrical noises within the casing. Also, in some watches the case is made of a plastic or other insulating material which permits electromagnetic waves to pass through. This increases the possibility of introducing noises, that is, erroneous signals into the input of the switch circuit.
What is needed is an anti-chatter circuit which discriminates between true switch closings and undesired electrical noise signals which can actuate the circuitry associated with the switch .